1. Field of the Invention
This invention relates to a mimeographic printing machine including a rotary cylindrical drum on which a stencil is to be wound along the outer circumferential surface.
2. Description of the Related Art
A mimeographic printing machine is currently known which includes a rotary cylindrical drum for supporting on its outer circumferential surface a stencil, and a lower pusher roller located under the cylindrical drum for holding a paper sheet between the cylindrical drum and the lower pusher roller to move the paper sheet forwardly during printing. FIG. 5 of the accompanying drawings shows such a mimeographic printing machine which includes an inside pusher roller 101 located inside a rotary cylindrical drum 100. This inside pusher roller 101, which is disclosed such as in co-assigned Japanese Patent Application No. 28553/1988, is located inside the cylindrical drum 100 for pushing the cylindrical drum 100 on the inner circumferential surface thereof to bring the outer circumferential surface of the cylindrical drum 100 against a lower pusher roller 102.
The cylindrical drum 100 is rotatably supported on a stationary center axis 103 to which an attachment plate 104 is fixedly attached inside the cylindrical drum 100. The inside pusher roller 101 is vertically movably attached to the attachment plate 104 via a pair of arms 105, 105 (only one shown) and is engageable with the inner circumferential surface of the cylindrical drum 100. A pair of springs (only one shown) 106, 106 is connected between the attachment plate 104 and each of the arms 105, which rotatably supports the opposite ends of the inside pusher roller 101, and normally urges the inside pusher roller 101 downwardly.
Though there is no illustration in the drawings, this machine has a retainer device for retaining the inside pusher roller 101 in an upper position remote from the cylindrical drum 100 against the bias of the springs 106, 106. When printing, the cylindrical drum 100 is driven for rotation, and the non-illustrated retainer device and the like are activated at a suitable timing; only when a print sheet 107 is supplied to the cylindrical drum 100, the inside pusher roller 101 is pushed against the inner circumferential surface of the cylindrical drum 101 under the bias of the spring 106, 106. At that time, the outer circumferential surface of the cylindrical drum 100 projects outwardly to press the paper sheet 107 against the lower pusher roller 102 so that an original image of the stencil is transferred to the paper sheet 107 with ink supplied from inside the cylindrical drum 100 through the original-image-pattern pores of the stencil.
With the above structure in which the inside pusher roller 101 is pressed against the cylindrical drum 100 by means of the springs 106, the biasing force of the springs 106 normally acts on the joints between the arms 105 and the attachment plate 104 and between the attachment plate 104 and the springs 106. Consequently, the associated parts or elements around the inside pusher roller 101 over which the spring force extends should currently be adequately strong and hence were large in weight, resulting in an increased cost of production. Further, it was very difficult to balance the resiliencies of the two springs 106, 106 at the opposite ends of the inside pusher roller 101 so that the density of print will hardly be uniform in the axial direction of the cylindrical drum 100.